The present invention relates to a head seek control method suppressing vibrations and to a rotary recorder/reproducer.
As a method of controlling a position of a head in a rotary recorder/reproducer such as a hard disk drive (HDD), there have been known the one-degree-of-freedom control in which only feedback control is employed, and the two-degree-of-freedom control in which, in addition to a feedback signal, also a feed-forward signal is used for control. In the two-degree-of-freedom control, the target value response performance (seek performance) is realized mainly with the feed-forward signal, and the external disturbance response performance (following performance) is realized with the feed-back signal. Because of this feature, the two performances can be optimized independently, which enables improvement in the control performance or in the response performance. Therefore, now the two-degree-of-freedom control is more and more widely employed for controlling a position of an HDD head, for which shortening of the head seek time is now strongly required.
In relation to the seek performance relating to high-speed movement of a head to a target track in an HDD, when high-speed seek is performed, vibrations occur in an actuator. In this case, attenuation of the excited vibrations is required to position a head on the target track, the seek time is delayed by the time required for waiting attenuation of the vibration. Further the excited vibrations are propagated to a cover, and sometimes acoustic noise is disadvantageously generated due to the vibrations of the cover.
To overcome the problems, an approach has been disclosed to smoothing a current waveform by feed forwarding with a polynomial function of high degree for time (refer to non-patent document 1: IEEE Transaction on Magnetics, Vol. 32, No. 3, May, 1996, pp 1793-1798). With this method, it is possible to suppress high frequency vibrations mainly caused by vibrations of the actuator, and also to reduce the acoustic noise caused by the vibrations.
Further an approach has been disclosed to smoothing a feed-forward current waveform with a short wavelength with an FIR filter in a short seek distance which is one hundredth of the maximum seek distance or below in patent document 1 (Japanese Patent Laid-open No. 2002-258902). In this document, a seek operation for 64 tracks is disclosed as an example.